Method of fastening drive elements of a hollow shaft

ABSTRACT

Method fastening drive elements on a hollow shaft, which comprises: 
     pushing n drive elements with a thickness a over a hollow shaft, retaining the drive elements at mutual spacings b and in respective desired azimuthal positions by means of holding devices; 
     providing active sections of a material with a given limit of elasticity, a length c, mutual spacings d and being bounded by sealing lips on a hydraulic expanding device so that .[.n (a+b)=n (c+d).]. .Iadd.n.a+(n-1) b=n.c+(n-1) d.Iaddend., pushing the hydraulic expanding device into the hollow shaft; and 
     applying a pressure through the hollow shaft to the active sections stressing the material of the active sections radially beyond the given limit of elasticity.

The invention relates to a method of fastening drive elements on ahollow shaft.

The method is described below by using an example of a cam shaft forfour-cycle internal combustion engines, but it is similarly applicableto other drive elements, such gears, bearing shells and the like whichare to be fastened to a smooth shaft, so as to be secure againstrotation and axial shifting. Although numerous fastening possibilitiesare known from German Published, Non-Prosecuted Application No. DE-OS 2336 241, they appear to be too costly to be used for mass production.

It is accordingly an object of the invention to provide a method offastening drive elements on a hollow shaft, which overcomes thehereinafore-mentioned disadvantages of the heretofore-known devices ofthis general type, and which permits a maximum number of drive elementsto be simultaneously fastened on a shaft with a minimum number ofoperations. Instead of expensive turned parts, less expensivelyproducible precision tubing is to be used for the shafts, and machiningand heat treating operations which may be required on the drive elementsthemselves should be performed prior to the actual assembly.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a method of fastening drive elements on ahollow shaft, which comprises:

pushing n drive elements with a thickness a over a hollow shaft,retaining the drive elements at mutual spacings b and in respectivedesired azimuthal positions to be assumed by means of holding devices;providing active sections of a material with a given limit ofelasticity, a length c, mutual spacings d and being bounded by sealinglips on a hydraulic expanding device so that .[.n(a+b)=n(c+d).]..Iadd.n.a+(n-1)b=n.c+(n-1)d.Iaddend., pushing the hydraulic expandingdevice into the hollow shaft; and applying a pressure through the hollowshaft to the active sections stressing the material of the activesections radially beyond the given limit of elasticity.

Hydraulic expanding devices of this type are known in principle,although each has only one active section, e.g. for the fastening ofheat exchanger tubes in tube plates. The method according to theinvention is also well adapted to the pairing of materials such as arelatively tough, readily deformable shaft material with the highergrade, normally hardened material of the drive elements, which isdesirable for other reasons as well. It is not difficult to adapt thehydraulic expanding device to the number of drive elements to befastened on the shaft in one operation and to adapt it to their possiblyuneven mutual spacings.

In accordance with a concomitant mode of the invention, there isprovided a method which comprises making a=c or b=d. This method is usedbecause it appears advantageous to utilize the entire contact areabetween the drive elements and the associated shaft sections to producethe positive frictional connection.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a method of fastening drive elements on a hollow shaft, it isnevertheless not intended to be limited to the details shown, sincevarious modifications may be made therein without departing from thespirit of the invention and within the scope and range of equivalents ofthe claims.

The invention, however, together with additional objects and advantagesthereof will be best understood from the following description when readin connection with the accompanying drawings, in which:

FIG. 1 is a fragmentary, diagrammatic, axial, longitudinal sectionalview taken along the line I--I in FIG. 2, in the direction of thearrows; and

FIG. 2 is an elevational view as seen along the arrow II in FIG. 1.

Referring now to FIGS. 1 and 2 of the drawings in detail, there is seena cam shaft for a four-cylinder internal combustion engine such as isused in motor vehicles, having cylinders Z 1 to Z 4 with cams 1 whichcontrol intake valves and other cams Z which control outlet valves. Thecams are retained by an appropriate number of holding tools or devices 3which may be tong or clamp-shaped. The holding devices are inrespectively required azimuthal alignment, are accurately spaced axiallyand are coaxial. The cams or drive elements 1 and 2 are finished, i.e.ground and hardened. The cams or drive elements have a uniformthickness, but need not necessarily have the illustrated uniformity andare disposed at distances b₁, b₂, b₃ from each other, which may vary ifdesired. A hollow shaft 4 formed of a relatively tough steel is pushedthrough bores formed in the cams 1, 2 with a sightly larger diameterthan the shaft. A hydraulic expanding device 5 is pushed into the hollowshaft 4 when the shaft is pushed through the bores or in a secondoperation. In addition to conventional non-illustrated pressuregenerating devices, the expanding device 5 is formed of a tube 6 onwhich active sections are installed at varying distances (d₁, d₂, d₃corresponding to the mutual spacings of the cams or drive elements. Theactive sections have a width c which may be narrower than a width a ofthe cams as shown but preferably is the same. In the latter case, thedistances b₁, b₂, b₃ between the cams are naturally equal to thedistances d₁, d₂, d₃. The active sections are formed by elastic rings orsealing lips 7 which are inserted in pairs into grooves formed in thesurface of the tube 6. At least one hole 8 is provided in the tube 6between each two rings of a pair through which hydraulic fluid canescape into the space between the elements 7. The elements 7 areconstructed in such a way that they are slightly smaller than the insidediameter of the tube 4 in their relaxed state while contacting the innerwall surface of the tube 4 when pressure is applied, preventing theescape of the hydraulic fluid from the active sections to a largeextent. The hydraulic fluid pressure is sufficient to expand the tube 4in the vicinity of the active sections by exceeding the elasticitylimit. After the conclusion of this process in all of the activesections, the device 5 is simultaneously made pressureless again for alldrive elements and is pulled out of the tube 4. The holding devices 3can then be opened and the cam shaft can be transported to the locationof the next operation.

FIG. 2 shows the sectors associated with the individual cylinders Z 1AND Z 4 in which the valves associated with the cylinders must becontrolled and which accordingly determine the cam orientation.

The foregoing is a description corresponding in substance to GermanApplication No. P 35 30 600.9, filed Aug. 27, 1985, the Internationalpriority of which is being claimed for the instant application, andwhich is hereby made part of this application. Any materialdiscrepancies between the foregoing specification and theafore-mentioned corresponding German application are to be resolved infavor of the latter.

We claim:
 1. Method of fastening drive elements on a hollow shaft, whichcomprises:pushing .[.n.]. drive elements with a thickness .[.a.]. over ahollow shaft of a material with a given limit of elasticity, retainingthe drive elements at mutual spacings .[.b.]. and in respective desiredazimuthal positions by means of holding devices; providing .Iadd.ahydraulic expanding device having .Iaddend.active sections with a length.[.c.]., mutual spacings .[.d.]. and .[.being bounded by.]. sealing lips.[.on a hydraulic expanding device so that n(a+b)=n(c+d).]..Iadd.bounding the active sections.Iaddend., pushing the hydraulicexpanding device into the hollow shaft; applying a pressure through thehydraulic expanding device to the active sections stressing the materialof portions of the hollow shaft opposite the active sections radiallybeyond the given limit of elasticity and into secured engagement withthe drive elements; reducing the pressure at the active sections; andwithdrawing the hydraulic expanding device from the expanded hollowshaft.
 2. Method according to claim .[.1.]. .Iadd.4.Iaddend., whichcomprises making a=c. .[.3. Method according to claim 1, which comprisesmaking b=d.].. .Iadd.4. Method according to claim 1, which comprisesmaking n.a+(n-1)b=n.c+(n-1)d, wherein n is the number of drive elements,a is the thickness of the drive elements, b is the spacing between thedrive elements, c is the length of the active sections, and d is thespacing between the active sections.Iaddend..